Octane separation system and operating method

ABSTRACT

An engine method, comprising delivering high octane fuel to a high octane fuel tank and delivering low octane fuel to a low octane fuel tank and injecting atmospheric air into an exhaust system for secondary air injection in response to delivering low octane fuel to an engine.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 13/973,872, entitled “OCTANE SEPARATION SYSTEM AND OPERATINGMETHOD,” filed on Aug. 22, 2013, the entire contents of which are herebyincorporated by reference for all purposes.

BACKGROUND AND SUMMARY

Gasoline used in engine combustion contains a large number of compounds,typically including dozens or hundreds of hydrocarbons plus alcohol.Each of these compounds may have different energy densities and knockproperties or “octane” inherent to their chemical composition andstructure.

The octane of a fuel is the ease at which the fuel auto-ignites. Afuel's octane may be classified by its tendency to ignite under variablepressure or temperature conditions. An octane rating is a standardprocedure for quantifying the conditions at which a fuel auto-igniteswithout external ignition. Compounds with higher octane ratings maywithstand greater temperature within a combustion chamber withoutauto-igniting. High torque demands may be met by increased airflow intoa combustion chamber, thus a combustion chamber may have high pressureand temperature during high torque operation. If chamber conditionsreach the auto-ignition conditions of the air-fuel mixture locatedtherein, pre-ignition or engine knock may occur.

Hydrocarbon compounds having high octane ratings often have low energydensity. In general, the combustion of an amount of high octane fuelwill produce less energy than the combustion of the same amount of lowoctane fuel. Thus for a given energy demand, more high octane fuel isinjected into a combustion chamber than low octane fuel. Thus theprotective benefits of the high octane components of fuel are balancedwith the fuel efficiency losses from combustion of fuels that are notenergy dense.

Gasoline separation has been suggested as a means to address the aboveissues. Prior approaches have removed ethanol from blended fuel mixturesfor selective injection. Ethanol however, is just one of the many highoctane components of gasoline. Further, this method does not allow for avariable octane separation threshold.

Further approaches have separated the gasoline of an externally filledfuel tank into a low octane portion and a high octane portion storedseparately in a high octane fuel tank and a low octane fuel tank. Manyvehicles however have limited available space and therefore cannotaccommodate a three fuel tank and three fuel pump configuration.Further, this method adds additional weight to the vehicle contributingto fuel efficiency losses, and the method is also high cost.

The inventors herein found that by separating fuel by octane level, thedesired octane separation threshold may be set at a number of values toachieve precise combustion control. Further, by separating fuel into ahigh octane portion and a low octane portion and returning the lowoctane portion to the externally filled fuel tank (or vice versa) fuelseparation advantages may be achieved without adding a third fuel pumpand tank, lessening both the weight and space occupied by the separationsystem, and decreasing the system cost. A fuel separator may have ahigher low octane output or a higher high octane output. Thus theseparation tank may be smaller than the externally filled fuel tank andmay store the fuel with an octane rate corresponding to lower separatoroutput to further minimize the volume occupied by the separation systemand the system weight and to effectively transform the externally filledfuel tank into a high octane fuel tank or a low octane fuel tank.

An exemplary embodiment may deliver fuel from an externally filled fueltank to a separator where it may be separated into a low octane portionand a high octane portion. The high octane portion may be delivered tothe high octane storage tank and the low octane portion may be returnedto the externally filled fuel tank. The octane level within theexternally filled fuel tank may continuously decrease throughout fuelseparation and thus the octane level may be continuously monitored. Anoperating method may terminate fuel separation if the externally filledfuel tank's fuel level falls below a threshold or empties or if thesmaller high octane fuel tank is full. Further embodiments may terminateseparation if the octane level in the externally filled fuel tank fallsbelow a threshold.

Prior fuel separation approaches experience fuel staleness afterextended operation at a limited range of speed-loads. For example, thismay result from a vehicle being used for heavy towing or operated athigh power much more frequently than at lower power, thus low octanefuel may be used less frequently than high octane fuel. Alternatively, avehicle may be operated almost exclusively at idle and light loads, thushigh octane fuel may almost never be used. Therefore fuel in theunderused tank may become stale after a period of time. Disclosedembodiments decrease or eliminate fuel staleness by independentlymonitoring conditions contributing to fuel staleness within the separatetanks. If fuel is determined to be stale, fuel from the underused tankmay be delivered to the engine for combustion. Determination of fuelstaleness may be desired for any engine system which stores and uses twofuels independently. For example, it may be desired for a dual fuelgasoline+CNG engine, for a gasoline PFI+E85 DI engine, for a systemwhich uses onboard separation of ethanol from a gasoline-ethanol blend,etc.

The disclosed system is particularly well suited for systems equippedwith secondary air injection for fast catalyst light-off and emissionreduction. Exhaust gas enriched with an amount of low octane fuel may bemore readily combustible than exhaust gas enriched with high octanefuel. Thus, when secondary air injection is desired low octane fuel maybe used for increased secondary combustion efficiency.

In an exemplary embodiment, a system may have a high octane fuel tankand a low octane fuel tank and may be equipped with secondary airinjection for exhaust combustion. When secondary air injection isdesired an amount of low octane fuel delivered to the engine mayincrease. Similarly, if a high amount of low octane fuel is being usedfor combustion, secondary air injection may be initiated. Similaroperation may also be used to increase efficiency and reduce emissionsduring engine cold start.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION

FIG. 1 depicts an example embodiment of a combustion engine.

FIG. 2 depicts an example embodiment of a three-tank fuel system with afuel separator.

FIG. 3 depicts an example embodiment of a two-tank fuel system with afuel separator.

FIG. 4 depicts an additional example embodiment of a two-tank fuelsystem with a fuel separator and secondary air injection.

FIG. 5-FIG. 12 depict example operating methods for a fuel system withfuel separation.

FIG. 13-FIG. 15 depict example operating methods for a fuel system withfuel separation and secondary air injection.

DETAILED DESCRIPTION

Gasoline contains a large number of hydrocarbon compounds used forcombustion. Compounds such as isooctane (C₈H₁₈), butane (C₄H₁₀),3-ethyitoluene (C₉H₁₂), and octane enhancer methyl tert-butyl ether(C₅H₁₂O) are commonly found in gasoline, each having a respective octanerating and energy density. Ethanol (C₂H₆O) is also commonly found inblended gasoline and has a higher octane rating and lower energy densitythan unblended gasoline.

Octane rating and, synonymously, octane level refer to conditions that afuel-air mixture can withstand without igniting. Higher octane fuels maywithstand higher pressure and temperature within a combustion chamberwithout auto-igniting than lower octane fuels.

Under normal applied ignition conditions, combustion is initiated in acombustion chamber via a spark containing an air fuel mixture between 10and 40 crankshaft degrees prior to top dead center. This allows for thecombustion process to develop peak pressure at a time allowing formaximum recovery of work from the expanding gas. A flame frontoriginating at the spark location accelerates through the air fuelmixture, rapidly increasing the pressure and temperature within thefuel-air mixture. Pressure then drops when the piston descends, andpressure energy is transformed into mechanical work and eventuallyengine torque.

During the high pressure portion of the piston cycle, the pressure andtemperature within the cylinder may exceed the ignition threshold of thefuel-air mixture within the chamber. This may cause detonation within anair/fuel pocket outside of the flame front, called engine knocking.Engine knocking may cause objectionable noise, and severe or extendedknock causes thermo-mechanical damage to the engine as well as a loss offuel efficiency. The propensity for engine knocking may be decreased bylowering the heat of combustion or the pressure within the enginecylinders, however, this limits available torque. Pre-ignition occurswhen the temperature or pressure within an engine cylinder causes theair-fuel mixture to ignite prior to ignition application.

Higher octane fuels are less likely to cause engine knocking orpre-ignition due to their heightened detonation threshold. Thus inconditions conducive to engine knock, such as high engine temperature orhigh aircharge pressure, high octane fuels may be desirable forinjection into engine cylinders.

Energy density refers to the amount of energy a fuel releases duringcombustion. During combustion, thermal energy from the fuel may betransformed into piston work. Fuels with higher energy densities mayexpel more energy per unit mass or volume than fuels with lower energydensities. Thus a larger amount of low energy density fuel may beexpended than high energy density fuel for a given torque output. Thusfuel with low energy density may contribute to fuel efficiency lossesand heightened emissions.

An embodiment may optimize the advantages associated with both fueltypes by selectively injecting high octane fuel during operationconducive to engine knock, and injecting low octane fuel for heightenedefficiency.

In an embodiment, gasoline in an externally filled fuel tank may includea mixture of high octane and low octane compounds. An externally filledfuel tank may refer to the fuel tank coupled to the outside of thevehicle for direct delivery of fuel from a user by inserting a fuelnozzle into a fill neck. A fuel separator may be fluidically coupled tothe externally filled fuel tank via a fuel pump located within a fueldelivery line. A fuel separator embodiment may include a containmentvessel with a membrane located therein separating the containment vesselinto a high octane portion and a low octane portion. Each portion mayhave a respective fuel outlet. A membrane may allow the selectivepermeation of some of the components contained within gasoline. Each ofthe two sides of the containment vessel may be maintained at respectivepressures.

A side of the vessel coupled to the externally filled fuel tank may bemaintained at a pressure higher than its opposite side. The highpressure side receiving fuel from the externally filled fuel tank maycorrespond with the low octane fuel side of the separator. Higher octanecompounds may permeate through the membrane to the lower pressure sideof the separator in a vaporous form.

The pressure within the high pressure side of the separator may be abovea vapor pressure of high octane gasoline components and below a vaporpressure of low octane gasoline components. The octane level ofgasoline's compounds may be proportional to the vapor pressure of thecompounds. In other words, at a separator pressure, higher octanecompounds may vaporize at a greater rate than low octane compoundscreating a more high octane fuel and a more low octane fuel within aseparator.

In an embodiment, fuel vapor on the low pressure side of the membranemay be collected in a secondary containment vessel where it may becondensed to a liquid state. For the reasons stated above, the octanelevel of condensed vapor may be higher than the octane level of the fuelremaining in the higher pressure side of the separator as well as theaverage octane level of the gasoline remaining in the externally filledfuel tank.

The rate at which gasoline vaporizes may be determined by the pressureat which the high and low pressure portions of the separator aremaintained. It may also be proportional to an amount of time gasolineremains in the separator or the rate at which fuel is cycled through theseparator. Thus in an embodiment, the high pressure side may be at apressure such that the liquid volume of fuel permeated through themembrane is greater than the liquid volume of fuel remaining in the highpressure side or vice versa.

In an embodiment, high octane fuel may be stored in a high octane fueltank and low octane fuel may be stored in a low octane fuel tank. Eachtank may be coupled to the high octane portion of the fuel separator andthe low octane portion of the fuel separator respectively. One or morefuel pumps may be operatively located between an externally filled fueltank and the fuel separator, between the fuel separator and the highoctane fuel tank, and between the fuel separator and the low octane fueltank. Fuel pumps may accelerate fuel between the tanks and theseparator.

In alternate embodiments, either the high octane port of the fuelseparator or the low octane port of the fuel separator may be coupled toan inlet port of the externally filled fuel tank via a return line. Inthis embodiment, one of the additional separation tanks and respectivepumps is eliminated, reducing the required packaging space and vehicleweight in comparison to the aforementioned embodiment. Consequentially,following a fuel refill event, the octane level in the externally filledfuel tank becomes increasingly higher or lower such that, after a time,the externally filled fuel tank becomes a high octane or low octane fueltank.

In an embodiment, the high octane fuel tank and the low octane fuel tankmay be separately coupled to the engine. The high and low octane fueltank may have respective fuel lines fluidically coupled to a number offuel injectors. In a dual direct injection embodiment, each cylinder mayhave a low octane fuel injector and a high octane fuel injector locatedon the periphery of each engine cylinder for injecting fuel directlyinto a combustion chamber.

In a still further embodiment, fuel lines may combine upstream of thefuel injectors. A valve may couple the high octane fuel line and the lowoctane fuel line to a combined fuel line. The valve may be actuated toselect the octane level of fuel injected into the engine via a singleset of fuel injectors.

Further embodiments may utilize port injection. In a port injectionsystem one or more injectors at an intake port may inject fuel intointake air upstream of the engine cylinder. Some embodiments may haveseparate high octane and low octane injectors fluidically coupled to thehigh octane and low octane fuel tank respectively. Further embodimentsmay couple the high octane and low octane fuel lines upstream of theport fuel injectors.

Still further embodiments may have both port and direct injectors. Insome embodiments, a port injector and a direct injector may both befluidically coupled to a combined fuel line receiving relative amountsof high octane and low octane fuel. Embodiments may include a highoctane port fuel injector, a low octane port fuel injector, a highoctane direct injector, a low octane direct injector or some combinationthereof. For example, a high octane injector may be coupled to eachengine cylinder directly for increased knock suppression. A low octaneinjector may be a port injector to achieve improved air fuel mixing andpart load pumping work.

Delivery of fuel to an injector via a fuel line and/or the activation ofan injector may be controlled by a control system in response tooperating conditions in embodiments. Operating tendencies of a drivermay result in a disproportionate injection of high octane and low octanefuel. For example, a vehicle regularly operated at low engine speeds andgentle acceleration may rarely push the engine into higher engine loads,and may consequently rarely use high octane fuel. For this reason, highoctane fuel within the high octane fuel tank may not be used regularlyand may become stale. In another example, a vehicle operated regularlyat high engine loads and high engine speeds, this may result in highoctane fuel being injected into the engine more frequently than lowoctane fuel and low octane fuel may become stale.

Fuel staleness may refer to a number of fuel conditions that may resultfrom fuel remaining in a fuel tank for an extended period of time. Theshelf life of fuel is limited for a number of reasons. Staleness mayinclude evaporation staleness, oxidation staleness, condensationstaleness, and/or seasonal staleness. For example, the more volatilecomponents of fuel may evaporate out of the fuel into the air within thefuel storage container, and be captured by the evaporative emissionssystem. This leads to degraded fuel evaporation and mixing, which mayresult in degraded engine starts and increased emissions. Hydrocarbonswithin fuel may also oxidize if left to sit in a fuel tank. Oxidationreduces fuel efficiency and may cause gasoline to congeal. Congealedgasoline may clog fuel filters and injectors leading to increased fueldegradation and decreased performance. Diurnal cycles may also causehumid air to contaminate the fuel system due to temperature fluctuationscausing humidity in air to condense which, in turn, may cause freezingand dilution of fuel, and rust and corrosion within the fuel system.

For the purposes of this disclosure, fuel staleness may also refer tofuel having an inappropriate seasonal grade. Federal emissionsregulations mandate the reformulation of gasoline fuel sold at pumps toreduce the content of toxic and ozone-forming compounds in vehicleemissions. For example, to reduce the emission of volatile organiccompounds (VOC), fuels sold in southern areas (e.g., areas categorizedunder ASTM class B) may be required to have a lower Reid vapor pressure(RVP) as compared to fuels sold in northern areas (e.g., areascategorized under ASTM class C) during summer months. Specifically, thedifferences in climate between the two types of areas may require acorresponding difference in the gasoline fuel volatility to achieve thesame emissions effect.

Other fuel parameters and fuel additives that affect vehicle emissionsinclude the Reid vapor pressure (RVP) of the fuel, fuel oxygen, benzeneand aromatics content, as well as the presence of sulfur, T90 (or E300),olefins, and T50 (or E200). To control the emissions of volatile organiccompounds (VOC), fuel RVP and oxygen specifications have been mandatedby the EPA. For example, fuels sold during high ozone (or summer)seasons (that is, from June 1 through September 15), are required tohave an RVP of no more than 7.2 psi in southern areas (that is, VOCcontrol region 1, or ASTM class B during summer) and 8.1 psi in northernareas (that is, VOC control region 2, or ASTM class C during summer).The difference in climate between the two areas requires a correspondingdifference in fuel (e.g., gasoline) volatility to achieve the sameemissions effect. As such, the high ozone season is selected to be June1-September 15 by the EPA as most ozone violations occur during thisperiod. Since fuels with higher RVP evaporate more easily than fuelswith lower RVP, by mandating a fuel with a lower RVP during summerseasons, the VOC emissions of the summer-grade fuel can be decreased,and ozone violations can be reduced.

Fuel produced during the winter may have higher levels of butane thanfuel produced during the summer due to the reduced engine performance incold atmospheric conditions. Thus, the fuel produced during the summermay decrease engine performance if used during winter temperatures. Thismay be most apparent during engine cold start and may increase the timeit takes an engine to reach its ideal operating temperature, leading toincreased emissions and decreased efficiency. Therefore, fuel remainingin an underutilized high or low octane fuel tank may be of aninappropriate seasonal grade and may contribute to operational lossesand increased emissions.

In an exemplary embodiment, emissions may be decreased by injecting anamount of atmospheric air into an exhaust manifold in a relatively hotportion of the exhaust system.

In an embodiment utilizing secondary air injection, the fuel-air mixturein the cylinders is intentionally rich, and atmospheric air is injectedinto the engine exhaust system. Oxygen within the air may oxidize orburn unburnt hydrocarbons remaining in the exhaust, thus increasingexhaust temperature for fast catalyst light-off while reducing thehydrocarbon content of emitted exhaust.

At high exhaust temperatures, secondary air injection may be moreeffective. Therefore, when secondary air injection is desired, thetemperature of exhaust gas may be increased. One example method toincrease the temperature includes increasing spark retard. High sparkretard allows for exhaust gas to escape a combustion chamber withdecreased temperature drop. However, less work may be captured byexpanding gas in a piston cycle resulting in engine efficiency andperformance losses. Other embodiments may use increased enrichment toincrease oxidation with secondary air, however, this may lead todecreased fuel efficiency and may adversely affect the emissionadvantages associated with secondary air injection.

Some hydrocarbons may be easier to oxidize within secondary airinjection. For example, low octane compounds may be more volatile thantheir high octane counterparts. Exhaust gas rich in low octane fuel maytherefore achieve efficient secondary air oxidation with less enrichmentor decreased spark retard than exhaust gas rich in high octane fuel.

Thus, in an embodiment, an amount of spark retard may be reduced whenlow octane fuel is being injected from a fuel separation systemutilizing secondary air injection. Alternately, when the fuel injectedinto the engine has a high octane level, and thus the compounds withinexhaust gas have a higher octane level, spark retard may be increased soas to achieve desirable hydrocarbon oxidation during secondary airinjection. In another example, when low octane fuel is being injectedinto the engine at a high rate, secondary air injection may be initiatedand when high octane fuel is being injected into the engine, secondaryair injection may be decreased or terminated. Thus the efficiency andperformances losses associated with secondary air injection may beminimized in a system with selective octane level fuel injection.

In further embodiments, when secondary air injection is initiated ordesired, an amount of low octane fuel delivered to the engine mayincreased and an amount of high octane fuel may be decreased.

FIG. 1 is a schematic diagram showing one cylinder of multi-cylinderengine 10, which may be included in a propulsion system of anautomobile. The engine may be fuel via natural gas, gasoline, or both. Acontrol system may control engine operation via controller 12 that maybe responsive to various sensors within the engine system and input fromvehicle operator 132 via an input device 130. Input device 130 mayinclude an accelerator pedal and a pedal position sensor 134 forgenerating a proportional pedal position signal PP. Cylinder 30 ofengine 10 may exist between cylinder walls 32 and piston 36 may bepositioned therein. Piston 36 may be coupled to crankshaft 40 so thatreciprocating motion of the piston is translated into rotational motionof the crankshaft. Crankshaft 40 may be coupled to at least one drivewheel of a vehicle via an intermediate transmission system.

Cylinder 30 may receive intake air from intake manifold 44 via intakepassage 42 and may exhaust combustion gases via exhaust passage 48.

Intake manifold 44 and exhaust passage 48 may selectively communicatewith cylinder 30 via respective intake valve 52 and exhaust valve 54. Insome embodiments, cylinder 30 may include two or more intake valvesand/or two or more exhaust valves.

In this example, intake valve 52 and exhaust valves 54 may be controlledby cam actuation via respective cam actuation systems 51 and 53. Camactuation systems 51 and 53 may each include one or more cams and mayutilize one or more of cam profile switching (CPS), variable cam timing(VCT), variable valve timing (VVT) and/or variable valve lift (VVL)systems that may be operated by controller 12 to vary valve operation.The position of intake valve 52 and exhaust valve 54 may be determinedby position sensors 55 and 57, respectively. In alternative embodiments,intake valve 52 and/or exhaust valve 54 may be controlled by electricvalve actuation. For example, a cylinder may include an intake valvecontrolled via electric valve actuation and an exhaust valve controlledvia cam actuation.

Fuel injector 66 is shown coupled directly to cylinder 30 for injectingfuel directly therein. An amount of fuel injection may be proportionalto pulse width of signal FPW received from controller 12 via electronicdriver 68. In this manner, fuel injector 66 provides what is known asdirect injection of fuel into cylinder 30. The fuel injector may bemounted in the side of the cylinder or in the top of the cylinder, forexample. Fuel may be delivered to fuel injector 66 by a fuel system (notshown) including a fuel tank, a fuel pump, and a fuel rail. In someembodiments, cylinder 30 may alternatively or additionally include afuel injector arranged in intake manifold 44 in a port injectionconfiguration.

Injected fuel may be natural gas or liquid gasoline such as petroleum ordiesel. Some embodiments may include both a natural gas fuel injectorand a liquid gasoline fuel injector. In primarily natural gas engines,gasoline may be injected in the absence of available NG. Otherembodiments may inject gasoline in response to operating conditions suchas high engine temperature, pre-ignition, or engine knock indication.

Intake passage 42 may include a throttle 62 having a throttle plate 64.The position of throttle plate 64 may be varied by controller 12 via asignal provided to an electric motor or actuator in an electronicthrottle control (ETC) configuration. In this manner, throttle 62 may beoperated to vary the intake air provided to cylinder 30 among otherengine cylinders. The position of throttle plate 64 may be provided tocontroller 12 by throttle position signal TP. Intake passage 42 mayinclude a mass air flow sensor 120 and a manifold air pressure sensor122 for providing respective signals MAF and MAP to controller 12.

Ignition system 88 may provide an ignition spark to cylinder 30 viaspark plug 82 in response to spark advance signal SA from controller 12.In some embodiments, one or more other cylinders of engine 10 may beoperated in a compression ignition mode, with or without an ignitionspark.

Exhaust gas sensor 126 is shown coupled to exhaust passage 48 upstreamof emission control device 70. Sensor 126 may be a suitable sensor forproviding an indication of exhaust gas air/fuel ratio such as a linearoxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), atwo-state oxygen sensor or EGO, a HEGO (heated EGO), a NOx, HC, or COsensor. Emission control device 70 is shown arranged along exhaustpassage 48 downstream of exhaust gas sensor 126. Device 70 may be athree way catalyst (TWC), NOx trap, various other emission controldevices, or combinations thereof. In some embodiments, emission controldevice 70 may be periodically regenerated during operation of engine 10by operating at least one cylinder of the engine within a particularair/fuel ratio resulting in heightened heat generation.

Engine 10 may further include a compression device such as aturbocharger or supercharger wherein a compressor is arranged alongintake manifold. For a turbocharger, a compressor may be at leastpartially driven by a turbine (e.g. via a shaft) arranged along anexhaust passage. One or more of a wastegate and a compressor bypassvalve may also be included to control flow through the turbine andcompressor. For a supercharger, a compressor may be at least partiallydriven by the engine and/or an electric machine, and may not include aturbine. Thus, the amount of compression provided to one or morecylinders of the engine via a turbocharger or supercharger may be variedby controller 12.

Controller 12 is shown in FIG. 1 as a microcomputer, comprisingmicroprocessor unit 102, input/output ports 104, an electronic storagemedium for executable programs and calibration values shown as read-onlymemory 106, random access memory 108, keep alive memory 110, and a databus. Controller 12 may receive various signals from sensors coupled toengine 10, in addition to those signals previously discussed, includingmeasurement of inducted mass air flow (MAF) from mass air flow sensor120; engine coolant temperature (ECT) from temperature sensor 112coupled to cooling sleeve 114; a profile ignition pickup signal (PIP)from Hall effect sensor 118 (or other type) coupled to crankshaft 40;throttle position (TP) from a throttle position sensor; and absolutemanifold pressure signal, MAP, from sensor 122. Engine speed signal,RPM, may be generated by controller 12 from signal PIP. Manifoldpressure signal MAP from a manifold pressure sensor may be used toprovide an indication of vacuum, or pressure, in the intake manifold.Note that various combinations of the above sensors may be used.

Storage medium read-only memory 106 may be programmed with computerreadable data with instructions executable by CPU 102 for performingdisclosed and other methods.

As described above, FIG. 1 shows one cylinder of a multi-cylinderengine, and each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector, additive injector, spark plug,etc.

FIG. 2 schematically depicts an exemplary fuel system equipped with fuelseparation for a four cylinder combustion engine. Cylinders 30 may beconfigured as part of a cylinder head. In FIG. 2, the cylinder head isshown with 4 cylinders in an inline configuration. In some examples, acylinder head may have more or fewer cylinders, for example sixcylinders. In some examples, the cylinders may be arranged in a Vconfiguration or other suitable configuration.

The cylinders 30 are shown coupled to fuel system 230. Cylinder 30 isshown coupled to fuel injectors 224 and 226. In this embodiment, bothfuel injectors 224 and 226 inject fuel directly into a cylinder 30, eachcylinder having one or more respective injectors. Each fuel injector maybe configured to deliver a specific quantity of fuel at a specific pointin the engine cycle in response to commands from controller 12. One orboth fuel injectors may be utilized to deliver combustible fuel tocylinder 30 during each combustion cycle. The timing and quantity offuel injection may be controlled as a function of engine operatingconditions. Control of the timing and quantity of fuel injection will befurther discussed below and with regards to FIGS. 5-18.

Externally filled fuel tank 206 is shown with an amount of gasolinelocated therein. A fill neck 202 may allow for fuel to be periodicallyreplenished from a source outside of the vehicle. Fill neck 202 may bedirectly coupled to an outer side panel of the vehicle. The fill neckmay have a fuel inlet on the outer surface of the vehicle in which afuel nozzle may be inserted, the fill neck may have an outlet within theexternally filled fuel tank where fuel added via the inlet may bedeposited and stored. Externally filled fuel tank 206 may have a sensor204. Sensor 204 may be communicatively coupled to a control system andmay measure octane level, fuel volatility, or fuel level, for example.

A fuel pump 214 may be located within a delivery line 215 (or insidetank 206) and may accelerate fuel within delivery line 215 fromexternally filled fuel tank 206 to fuel separator 210. Delivery line 215may couple externally filled fuel tank 206 to the fuel separator aloneand may not be directly coupled to any other fuel tanks. Delivery line215 may supply fuel in one direction: from the externally filled fueltank 206 to the fuel separator 210 and thus may not receive fuel orgasoline from any source other than externally filled fuel tank 206.Pump 214 may accelerate fuel into a high pressure side 242 of fuelseparator 210. The high pressure side may be maintained at a pressureabove a vapor pressure of one or more compounds of gasoline. A lowpressure side 240 of separator 210 may be maintained at a pressure belowthat of high pressure side 242. The high pressure side 242 may beseparated from a low pressure side 240 by a membrane 212. Membrane 212may be a selectively permeable membrane that may allow some compounds topermeate into low pressure side 240. High octane components withingasoline may permeate across the membrane 212 more readily than lowoctane compounds. Compounds permeating across membrane 212 may be in avaporous form. The vapor may be condensed into a liquid in part of lowpressure side 240 or in an external vessel (not shown).

Low pressure side 240 may be coupled at a high octane outlet to a highoctane fuel tank 218 via fuel pump 216. High pressure side 242 may becoupled at a low octane outlet to a low octane fuel tank 219 via a fuelpump 217.

High octane fuel tank 218 may not directly receive fuel from any sourceother than fuel separator 210 and may be located along first fuel line232. Further, unlike externally filled fuel tank 206, high octane fueltank 218 may not receive fuel from a source outside of the vehicle andmay not be filled by a user or coupled to the outside of the vehicle.First fuel line 232 may carry fuel in one direction: from fuel separator210 to first fuel rail 236. Low octane fuel tank 219 may not directlyreceive fuel from any source other than fuel separator 210 and may belocated along second fuel line 234. Further, unlike externally filledfuel tank 206, low octane fuel tank 219 may not receive fuel from asource outside of the vehicle and may not be filled by a user or becoupled to the outside of the vehicle. Second fuel line 234 may carryfuel in one direction: from fuel separator 210 to second fuel rail 238.

Fuel injectors 224 are shown coupled to first fuel rail 236. Fuel rail236 may be fluidically coupled to a first fuel line 232. First fuel line232 may be fluidically coupled to high octane fuel tank 218. Fuel valve222 may be fluidically coupled to high octane fuel tank 218 and firstfuel line 232. First fuel rail 236 may include a plurality of sensors,including a temperature sensor and a pressure sensor. Similarly, firstfuel line 232 and high octane fuel tank 218 may include a plurality ofsensors, including temperature and pressure sensors. High octane fueltank 218 and low octane fuel tank 219 may have a smaller volume thanexternally filled fuel tank 206.

Valves 220 and 222 may be communicatively coupled to a control systemand may be independently actuated in response to engine operatingconditions and/or fuel conditions such as fuel level or staleness in theexternally filled fuel tank, the high octane fuel tank, or the lowoctane fuel tank. In some embodiments, valves 220 and/or 222 may not berequired.

First fuel line 232 may couple high octane fuel tank 218 to first fuelrail 236. First fuel rail 236 may run along cylinders 30 and may befluidically coupled to a number of fuel injectors corresponding to eachof cylinders 30. Second fuel line 234 may couple low octane fuel tank219 to second fuel rail 238. Second fuel rail 238 may run alongcylinders 30 and may be coupled to a number of fuel injectorscorresponding to each cylinder 30. Fuel injectors may be controlled by acontrol system and may inject fuel prior to ignition application. Theinjection of high octane fuel via injectors 224 and low octane fuel viainjectors 226 may be actuated by a control system in response to engineoperating conditions.

FIG. 3 schematically depicts an exemplary fuel system equipped with fuelseparation for a four cylinder engine system such as that depicted inFIG. 2.

The cylinders 30 are shown coupled to fuel system 230. Cylinders 30 areshown coupled to fuel injectors 226. In this example embodiment, fuelinjectors 226 inject fuel directly into cylinders 30, each cylinderhaving one or more respective injectors. Each fuel injector may beconfigured to deliver a specific quantity of fuel at a specific crankangle in response to commands from controller 12. The fuel injectors 226may deliver combustible fuel to cylinder 30 during each combustioncycle. The timing and quantity of fuel injection may be controlled as afunction of engine operating conditions.

Port fuel injectors 304 may be fluidically coupled to first fuel line232 such that the engine is equipped with both direct injection and portinjection. Port fuel injectors 304 may inject fuel into the intake portsupstream of the cylinders intake valves. Thus fuel may mix with airprior to induction into the cylinders. In comparison to directinjection, this may allow for fuel to be distributed more homogenouslythroughout an intake air stream prior to combustion.

Direct fuel injectors 226 may be fluidically coupled to high octane fueltank 218. Port fuel injectors 304 may be fluidically coupled to anexternally filled fuel tank 206 or a low octane fuel tank. To preventengine knock at high loads, high octane fuel may be injected directlyinto the cylinders to prevent auto-ignition. Direct injection of highoctane fuel may offer improved response times and higher precision thanport injection to effectively prevent engine knock. Port injectors 304may be fluidically coupled to a low octane fuel source such as anexternally filled fuel tank 206 or low octane fuel tank. Port injectionof a low octane and energy dense fuel allows for increased fuel to airmixing for efficient combustion. Thus direct injection of high octanefuel and port injection of low octane fuel may be used in combination inan embodiment.

Further embodiments may have both a low octane direct injector as wellas a high octane direct injector. Still further embodiments may haveboth a low octane port injector as well as a high octane port injector.Thus a control system may determine an amount of low octane fuel and anamount of high octane fuel to inject into the intake ports in responseto operating conditions. Further, a control system may determine anamount of high octane fuel and an amount of low octane fuel to injectdirectly into the engine cylinders in response to operating conditions.For example, a control system may determine a high octane to low octaneratio to achieve a first octane level for port injection and second highoctane to low octane ratio to achieve a second octane level for directinjection.

In further examples, the high octane fuel line may merge with the lowoctane fuel line upstream of a port or direct injector. An amount ofhigh octane fuel and low octane fuel delivered to the merged fuel linemay be in response to engine operating conditions via one or more valvesat a merge point or upstream of a merge point within the high octaneand/or low octane fuel lines. In this embodiment, a single port injectorand a single direct injector may deliver either high octane fuel, lowoctane fuel, or some combination thereof to an intake port and to acylinder respectively.

Externally filled fuel tank 206 is shown with an amount of gasolinelocated therein. A refuel port with a fill neck 202 may allow for fuelto be periodically replenished. Externally filled fuel tank 206 may havea sensor 204. Sensor 204 may be communicatively coupled to a controlsystem and may measure octane level, fuel volatility, or fuel level, forexample. Controller 12 may actuate a valve within a delivery line 215that is delivering fuel to a fuel separator 210. A valve and/or pump 214may be utilized for metering, initiating, and terminating fuel delivery.

A fuel pump 214 may couple externally filled fuel tank 206 to fuelseparator 210. Pump 214 may accelerate fuel into a high pressure side242 of fuel separator 210. The high pressure side may be maintained at apressure above a vapor pressure of one or more compounds of gasoline. Alow pressure side 240 of separator 210 may be maintained at a pressurebelow that of high pressure side 242. The high pressure side 242 may beseparated from a low pressure side 240 by a membrane 212. Membrane 212may be a selectively permeable membrane that may allow some compounds topermeate into low pressure side 240. High octane components withingasoline may permeate across the membrane 212 more readily than lowoctane compounds. Compounds permeating across membrane 212 may be in avaporous form. The vapors may be condensed into a liquid in part of lowpressure side 240 or in an external vessel (not shown).

Low pressure side 240 may be coupled at a high octane outlet to a highoctane fuel tank 218 via fuel pump 216. High pressure side 242 may becoupled at a low octane outlet to externally filled fuel tank 206 viafuel line 310 and fuel pump 211.

Direct fuel injectors 226 are shown coupled to DI fuel rail 238. DI fuelrail 238 may be fluidically coupled to second fuel line 234. Second fuelline 234 may be fluidically coupled to high octane fuel tank 218. Fuelpump 216 may be fluidically coupled to high octane fuel tank 218 andsecond fuel line 234. DI fuel rail 238 may include a plurality ofsensors, including a temperature sensor and a pressure sensor. A fuelvalve 222, which may be a three way valve, may selectively couple secondfuel line 234 to either direct injectors 226 or port injectors 304.

Similarly, first fuel line 232 may include a plurality of sensors,including temperature and pressure sensors. High octane fuel tank 218may have a smaller volume than externally filled fuel tank 206.

A fuel separator may have a low octane outlet coupling a low octane sideof separator 210 to a fuel return line 310. Fuel may be acceleratedthrough return line 310 via fuel pump 211. Return line 310 may couple aside of a separator 210 to externally filled fuel tank 206. Low octanefuel may be circulated back into an externally filled fuel tank where itmay mix with gasoline.

Valves 308 and 222 may be communicatively coupled to a control systemand may be independently actuated in response to engine operatingconditions and/or fuel conditions such as fuel level or staleness in theexternally filled fuel tank, the high octane fuel tank, or the lowoctane fuel tank.

First fuel line 232 may couple the externally filled fuel tank 206 toport injectors 304 via fuel pump 213 and valve 308. Externally filledfuel tank 206 may be fluidically coupled to first fuel rail 236 via afirst fuel line 232. First fuel rail 236 may run along cylinders 30 andmay be fluidically coupled to a number of fuel injectors correspondingto each cylinder 30. Second fuel line 234 may couple high octane fueltank 218 to second (DI) fuel rail 238. First fuel rail 236 may run alongcylinders 30 and may be fluidically coupled to a number of fuelinjectors corresponding to each cylinder 30. Fuel injectors may becontrolled by a control system and may inject fuel prior to ignitionapplication. The injection of high octane fuel via injectors 226 and lowoctane fuel via injectors 304 may be actuated by a control system inresponse to engine operating conditions.

FIG. 4 depicts an embodiment with a fuel system 230 similar to that ofFIG. 3. The embodiment of FIG. 4 further includes a secondary airinjection system. In secondary air injection, atmospheric air may beinjected into an exhaust system. A secondary air injection system mayhave secondary air intake 404 coupled to an externally filled intakesystem for delivery of air to an intake manifold. In furtherembodiments, a secondary air injection system may have an independentsecondary air intake 404 for delivery of air to an exhaust system.

Secondary air intake 404 may have an air pump 408 that may beoperatively located in a secondary air intake. Air pump 408 may beactuated by a control system and may control an amount of air deliveredto an exhaust manifold for secondary combustion. An amount of airdelivered to an exhaust manifold 402 may be dependent on one or moreoperating conditions which may include an octane level of fuel beinginjected into an engine cylinder. For example, if catalyst lightoff isdesired and low octane fuel is being injected into an engine cylinder ata high rate, an amount of air delivered to an exhaust manifold mayincrease.

An exhaust pipe may be coupled to an exhaust manifold and may includeone or more turbines, emission control devices, and mufflers. An exhaustpipe may emit exhaust gases into the atmosphere. In some embodiments,exhaust gases may be recirculated, in part, back into the intake system.

FIG. 5 shows a flowchart depicting method 500 in accordance with thepresent disclosure. Method 500 may be carried out by controller 12.Method 500 may be used in a configuration such as that depicted in FIGS.1-4. Method 500 may be used in combination or may be a subroutine ofmethods that may or may not be otherwise indicated within thisdisclosure.

Method 500 may begin at 502 and may be initiated by an engine startingevent or a refueling event. A refueling event may comprise adding fuelto an externally filled fuel tank from an external source. At 504, fuelmay be delivered from an externally filled fuel tank to a fuel separatorvia a fuel delivery line that may contain a fuel pump. Here a separatormay be any type of fuel separator and may or may not be the separatordescribed above or an octane based separator. For example, a separatormay separate blended fuel into ethanol and gasoline without departingfrom the scope of this disclosure.

At 506 the fuel within the separator may be separated into a high octaneportion and a low octane portion. As described above, a separator mayseparate fuel based on octane level. In other embodiments, fuel may beseparated by other fuel characteristics that result in one portion ofthe separated fuel having a higher octane level than the other portionof the separated fuel. A high octane fuel and the low octane fuel may bephysically separated within the separator. In an embodiment, fuel may beseparated by a semi-permeable membrane, a physical barrier, a methodinvolving addition of water or other substance, or high octane fuel maybe in a more upper portion of the gasoline within the separator than lowoctane fuel or vice versa.

At 508, high octane fuel may be delivered to a high octane fuel tank. Insome embodiments, the high octane side of the fuel tank may have a firstoutlet. High octane fuel may, in some embodiments, be released from theseparator in a gaseous form. In such an embodiment, high octane fuel maybe condensed into a liquid state in a condenser separate from the highoctane fuel tank or within the high octane fuel tank.

In embodiments having an externally filled fuel tank with a refuel port,a high octane fuel tank, and a low octane fuel tank, the high octanefuel tank may receive high octane fuel at 508. In embodimentsrecirculating high octane fuel into the externally filled fuel tank, thehigh octane fuel tank may refer to the externally filled fuel tank.

At 510 low octane fuel may be delivered to a low octane fuel tank. Inembodiments having an externally filled fuel tank with a refuel port, ahigh octane fuel tank, and a low octane fuel tank the low octane fueltank may receive low octane fuel at 510. In embodiments recirculatinglow octane fuel into an externally filled fuel tank, the low octane fueltank may refer to the externally filled fuel tank.

For the purposes of this disclosure, high octane fuel refers to fuelthat may have an octane rating or an octane level above a threshold,wherein the octane rating may be an aggregate average of the compoundswithin the high octane fuel. Similarly, low octane fuel refers to fuelthat may have an octane rating or an octane level below a threshold,wherein the octane rating may be an aggregate average of the compoundswithin the low octane fuel. In other words, the high octane fuel, whentaken as a whole, may tend to auto-ignite less readily than the lowoctane fuel.

An octane rating may refer to a comparison of a test fuel to a fuelcontaining purely iso-octane and heptanes. For example, a fuel with anoctane rating of 70 may have the same detonation resistance of a fuelcombination that is 70% iso-octane and 30% heptane. Fuels with an octanerating above 100 exhibit greater detonation resistance than pure octane.Detonation resistance may be determined by a number of differentmethods. Though fuel measured by a first method may show a detonationresistance of a first iso-octane-heptane ratio, fuel measured by asecond method may show a detonation resistance of a secondiso-octane-heptane ratio. Thus each detonation resistance method yieldsdifferent octane numbers, three common octane numbers are ResearchOctane Number (RON), Motor Octane Number (MON), or an average of RON andMON called Anti-Knock Index (AKI).

Operating conditions may be determined at 512. Engine operatingconditions may be measured, estimated, or inferred, and may includevarious vehicle conditions, such as vehicle speed, as well as variousengine conditions, such as engine speed, engine temperature, exhausttemperature, boost level, MAP, MAF, torque demand, horsepower demand,etc. Determining engine operating conditions may include determiningwhether the engine is operating at a high load condition. Herein, a highload condition may be defined as a load that is greater than an upperthreshold, for example, 75% of maximum load, as compared to a load thatis greater than a lower threshold.

At 514 it may be determined if high octane fuel is desired within theengine. This determination may be made via another sub-routine that mayor may not be otherwise disclosed herein. High octane fuel may bedesired for a number of reasons including the engine load or speed beingabove a threshold, the temperature in the engine being above athreshold, the fuel level in a low octane fuel tank being below athreshold, the fuel level of the high octane fuel tank being below athreshold, the volume of air charge delivered to the engine cylindersbeing above a threshold, knock sensor signal being above a threshold,fuel staleness being above a threshold, or some combination thereof. Onesuch combination may determine that high octane fuel is desired if theengine is operating under conditions that may contribute to engineknock; this determination may be a function of several operatingconditions. If high octane fuel is desired, high octane fuel may bedelivered to an engine cylinder via the actuation of a fuel injectorand/or via the actuation of a valve and/or pump in a high octane fuelline or fuel rail.

In embodiments wherein the engine is coupled to a high octane fuel tank,a low octane fuel tank, and an externally filled fuel tank it may bedetermined if low octane fuel is desired at 520. Similar to step 514,low octane fuel octane fuel may be desired for a number of reasons. Iflow octane fuel is desired, method 500 may continue to 518. Inembodiments wherein two fuel tanks are coupled to engine, a ‘no’determination at 514 may proceed directly to the step at 518.

At 518, low octane fuel may be delivered to the engine. This may beinitiated via the actuation of one or more port and/or direct fuelinjectors and/or the actuation of a valve and/or pump in a low octanefuel line or fuel rail. Method 500 may repeat at given intervals orcontinuously throughout engine operation. Parts of method 500 may repeatindependently of other parts of method 500. For example, after an amountof fuel separation has occurred, steps 504-512 may repeat in rapidsuccession or at given intervals without regard to the steps below.Similarly, steps 514-520 may repeat with each injection of fuel into theengine, at given intervals, or in rapid succession without regard to thepreceding steps.

FIG. 6 shows a flowchart depicting method 600 in accordance with thepresent disclosure. Method 600 may be carried out by controller 12.Method 600 may be used in a configuration such as that depicted in FIGS.1-4. Method 600 may be used in combination or may be a subroutine ofmethods that may or may not be otherwise indicated within thisdisclosure.

Method 600 may begin at 602 and may be initiated by an engine startingevent or a refueling event. A refueling event may comprise adding fuelto the externally filled fuel tank from an external source. At 604 fuelmay be delivered from the externally filled fuel tank to a fuelseparator. Here a separator may be any type of fuel separator and may ormay not be the separator described above or an octane based separator.For example, a separator may separate blended fuel into ethanol andgasoline without departing from the scope of this disclosure.

At 606 the fuel within the separator may be separated into a high octaneportion and a low octane portion. As described above, a separator mayseparate fuel based on octane level. In other embodiments fuel may beseparated by other fuel characteristics that result in one portion ofthe separated fuel having a higher octane level than the other portionof the separated fuel. Within a fuel separator, at 606, the high octanefuel and the low octane fuel may be physically separated physicallocations within the compressor. In an embodiment, fuel may be separatedby a semi-permeable membrane, a physical barrier, or high octane fuelmay be in a more upper portion of the gasoline within the separator thanlow octane fuel or vice versa.

At 608, high octane fuel may be delivered to a high octane fuel tank. Insome embodiments, the high octane portion of the fuel separator may havea first outlet. High octane fuel may, in some embodiments, be releasedfrom the separator in a gaseous form. In such an embodiment, high octanefuel may be condensed into liquid form in a condenser separate from thehigh octane fuel tank or within the high octane fuel tank.

At 610, low octane fuel may be recirculated back into an externallyfilled fuel tank via a fuel return line. In embodiments having anexternally filled fuel tank with a refuel port and a high octane fueltank, the externally filled fuel tank may receive low octane fuel at610.

Operating conditions may be determined at 612. Engine operatingconditions may be measured, estimated, or inferred, and may includevarious vehicle conditions, such as vehicle speed, as well as variousengine operating conditions, such as engine speed, engine temperature,exhaust temperature, boost level, MAP, MAF, torque demand, horsepowerdemand, etc. Determining engine operating conditions may includedetermining whether the engine is operating at a high load condition.Herein, a high load condition may be defined as a load that is greaterthan an upper threshold, for example, 75% of maximum load, as comparedto a load that is greater than a lower threshold.

At 616 it may be determined if high octane fuel is desired within theengine. This determination may be made via another sub-routine that mayor may not be disclosed here. High octane fuel may be desired for anumber of reasons including the engine load or speed being above athreshold, the temperature in the engine being above a threshold, thefuel level in a low octane fuel tank being below a threshold, the fuellevel of the high octane fuel tank being below a threshold, the volumeof air charge delivered to the engine cylinders being above a threshold,knock sensor signal being above a threshold, fuel staleness being abovea threshold, or some combination thereof. One such combination maydetermine that high octane fuel is desired if the engine is operatingunder conditions that contribute to engine knock; this determination maybe a function of several operating conditions. If high octane fuel isdesired, high octane fuel may be delivered to an engine cylinder via theactuation of a fuel injector and/or via the actuation of a valve and/orpump in a high octane fuel line or fuel rail.

Method 600 may continue to 618 where fuel from the externally filledfuel tank may be injected into the engine. An amount of fuel deliveredfrom the externally filled fuel tank may be determined as a function ofoperating conditions, a desired octane level, the presiding octane levelwithin the externally filled fuel tank, the amount of high octane fueldelivered at 614, or some combinations thereof. In some embodiments nofuel may be injected into an engine at 618.

Delivery of high octane fuel and fuel from an externally filled fueltank may be initiated via the actuation of one or more port and/ordirect fuel injectors and/or the actuation of a valve and/or pump in alow or high octane fuel line or fuel rail. Method 600 may repeat atgiven intervals or continuously throughout engine operation. Parts ofmethod 600 may repeat independently of other parts of method 600. Forexample, after an amount of fuel separation has occurred, steps 604-610may repeat in rapid succession or at given intervals without regard tosuccessive steps. Similarly, steps 612-620 may repeat with eachinjection, at given intervals, or in rapid succession without regard tothe preceding steps.

FIG. 7 shows a flowchart depicting method 700 in accordance with thepresent disclosure. Method 700 may be carried out by controller 12.Method 700 may be used in a configuration such as that depicted in FIGS.1-4. Method 700 may be used in combination or may be a subroutine ofmethods that may or may not be otherwise indicated within thisdisclosure. For example, method 700 may be used in combination withmethod 500 and 600.

Method 700 may begin at 702 and may be initiated by an engine startingevent or a refueling event. A refueling event may comprise adding fuelto an externally filled fuel tank from an external source. At 704 it maybe determined if the externally filled fuel tank is empty. If theexternally filled fuel tank is not empty, it may be determined if a highor low octane fuel tank is empty. In embodiments having either a high orlow octane fuel tank and equipped with a return line, it may bedetermined if the fuel tank that is not the externally filled fuel tankis empty. In embodiments having both a high and low octane fuel tank aswell as an externally filled fuel tank, it may be determined if eitherthe high octane fuel tank or the low octane fuel tank is empty.

If the neither a high octane fuel tank, low octane fuel tank, orexternally filled fuel tank are empty, method 700 may move to 708. At708, fuel may be delivered from an externally filled fuel tank to a fuelseparator. Here a separator may be any type of fuel separator and may ormay not be the separator described above or an octane based separator.For example, a separator may separate blended fuel into ethanol andgasoline without departing from the scope of this disclosure.

At 710, the fuel within the separator may be separated into a highoctane portion and a low octane portion. As described above, a separatormay separate fuel based on octane level. In other embodiments fuel maybe separated by other fuel characteristics that result in one portion ofthe separated fuel having a higher octane level than the other portionof the separated fuel. At 710 the high octane fuel and the low octanefuel may be physically separated within the fuel separator. In anembodiment, fuel may be separated by a semi-permeable membrane, aphysical barrier, a method involving addition of water or othersubstance, or high octane fuel may be in a more upper portion of thegasoline within the separator than low octane fuel or vice versa.

At 712, high octane fuel may be delivered to a high octane fuel tank. Insome embodiments, the high octane portion of the fuel separator may havea first outlet. High octane fuel may, in some embodiments, be releasedfrom the separator in a gaseous form. In such an embodiment, high octanefuel may be condensed into liquid form in a condenser separate from thehigh octane fuel tank or within the high octane fuel tank.

In embodiments having an externally filled fuel tank with a refuel port,a high octane fuel tank, and a low octane fuel tank, the high octanefuel tank may receive high octane fuel at 712. In embodimentsrecirculating high octane fuel into an externally filled fuel tank, thehigh octane fuel tank may refer to the externally filled fuel tank. At714 low octane fuel may be delivered to a low octane fuel tank. Inembodiments having an externally filled fuel tank with a refuel port, ahigh octane fuel tank, and a low octane fuel tank the low octane fueltank may receive low octane fuel at 714. In embodiments recirculatinglow octane fuel into an externally filled fuel tank, the low octane fueltank may refer to the externally filled fuel tank. Method 700 may thencontinue to 716.

If it is determined at 704 or 706 that any of a high octane, low octane,or externally filled fuel tank is empty method 700 may continue directlyto 716.

Operating conditions may be determined at 716. Engine operatingconditions may be measured, estimated or inferred, and may includevarious vehicle conditions, such as vehicle speed, as well as variousengine operating conditions, such as engine speed, engine temperature,exhaust temperature, boost level, MAP, MAF, torque demand, horsepowerdemand, etc. Determining engine operating conditions may includedetermining whether the engine is operating at a high load condition.Herein, a high load condition may be defined as a load that is greaterthan an upper threshold, for example, 75% of maximum load, as comparedto a load that is greater than a lower threshold.

At 718 an amount of high octane fuel to be delivered to the engine forcombustion is determined. An amount of high octane fuel desired may bein response to several factors including engine load, engine speed,engine temperature, or a probability of engine knock. Probability ofengine knock may be determined in control system and may be based on oneor more operating conditions and/or based on a signal from a knocksensor. Further, an amount of high octane fuel delivered to the enginemay be a function of a high-octane-to-low-octane ratio with a desiredoctane level as determined in a control system.

At 720 an amount of low octane fuel to deliver to the engine forcombustion is determined. An amount of low octane fuel may be a functionof several factors including engine load, engine speed, enginetemperature, or a probability of engine knock. Further, an amount of lowoctane fuel delivered may be a function of a high-octane-to-low-octaneratio with a desired octane level as determined in a control system.

At 722, an amount of high octane fuel and low octane fuel determined at718 and 720 respectively is delivered to the engine. Delivery of highand low octane fuel may be initiated via the actuation of one or moreport and/or direct fuel injectors and/or the actuation of a valve and/orpump in a low or high octane fuel line or fuel rail. Method 700 mayrepeat at given intervals or in rapid succession throughout engineoperation.

FIG. 8 shows a flowchart depicting method 800 in accordance with thepresent disclosure. Method 800 may be carried out by controller 12.Method 800 may be used in a configuration such as that depicted in FIGS.1-4. Method 800 may be used in combination or may be a subroutine ofmethods that may or may not be otherwise indicated within thisdisclosure. For example, method 800 may be used in combination withmethod 500 and 600.

Method 800 may begin at 802 and may be initiated by an engine startingevent or a refueling event. A refueling event may comprise adding fuelto an externally filled fuel tank from an external source. A fuel systemmay be equipped with a fuel separator with a first outlet coupled to asecondary tank and a second outlet coupled to an externally filled fueltank with a refuel port via a return line. Fuel returned to theexternally filled fuel tank may be recirculated back through theseparator throughout operation, continuously removing high octanecompounds from the fuel in the externally filled fuel tank. Continuedfuel separation may then cause the fuel in the externally filled fueltank to drop to a very low aggregate octane level. Fuel with very lowoctane levels may not support even mid-range engine loads; this couldresult in degraded engine performance. Thus, fuel in a high octaneportion may be used to support mid-load operation and the octane levelwithin the externally filled fuel tank may continue to fall withcontinued separation before triggering a re-fuel event and significantperformance losses may be experienced. Thus by monitoring the octanelevel in an externally filled fuel tank, separation may be terminatedbefore reaching an undesirably low octane level.

At 803 the octane level in an externally filled fuel tank may bedetermined and compared to a threshold. A threshold may be predeterminedor decided by a controller and may be an octane level able to supportmid-load operation. If the octane level of fuel in the externally filledfuel tank is above a threshold the method may continue to 804. If theoctane level of fuel in an externally filled fuel tank is below athreshold the method may end. At 804 it may be determined if the levelof fuel in an externally filled fuel tank is above a threshold. This maybe a predetermined low fuel threshold or may correspond to an amount offuel in a secondary fuel tank. If the level of fuel is above thisthreshold the method may continue to 806. If the level of fuel in theexternally filled fuel tank is below this threshold the method may end.The externally filled fuel tank may be fluidically coupled to a fuelseparator. At 806, fuel may be delivered to the separator.

At 808 the fuel within the separator may be separated into a high octaneportion and a low octane portion. As described above, a separator mayseparate fuel based on octane level. In other embodiments fuel may beseparated by other fuel characteristics that result in one portion ofthe separated fuel having a higher octane level than the other portionof the separated fuel. Within a fuel separator, at 606 the high octanefuel and the low octane fuel may be physically separated within theseparator. In an embodiment, fuel may be separated by a semi-permeablemembrane, a physical barrier, a method involving addition of water orother substance, or high octane fuel may be in a more upper portion ofthe gasoline within the separator than low octane fuel or vice versa.

At 810, high octane fuel may be delivered to a high octane fuel tank. Insome embodiments, the high octane portion of the fuel separator may havea first outlet. High octane fuel may, in some embodiments, be releasedfrom the separator in a gaseous form. In such an embodiment, high octanefuel may be condensed into liquid form in a condenser separate from thehigh octane fuel tank or within the high octane fuel tank.

In embodiments recirculating high octane fuel into an externally filledfuel tank, the high octane fuel tank may refer to the externally filledfuel tank. Low octane fuel, as determined by the separator, may bereturned to an externally filled fuel tank via a return line. The cyclemay repeat until the octane level in the externally filled fuel tankfalls below the aforementioned threshold. If the octane level in theexternally filled fuel tank falls below an octane threshold at 802, fuelseparation may end. Separation may be reinitiated in response to anengine refueling event. Fuel separation may further be initiated by anengine starting event and may be terminated by an engine off event.

Presiding octane level in an externally filled fuel tank may bedetermined, in some embodiments, via a knock sensor system when fuelfrom the externally filled tank is being used. In other embodiments anoctane level may be inferred based on the amount of time separation hasoccurred or a volume of fuel passing through a separator or in a highoctane fuel tank. Other embodiments may determine a presiding octanelevel using a sensor or method not otherwise disclosed herein.

FIG. 9 shows a flowchart depicting method 900 in accordance with thepresent disclosure. Method 900 may be carried out by controller 12.Method 900 may be used in a configuration such as that depicted in FIGS.1-4. Method 900 may be used in combination or may be a subroutine ofmethods that may or may not be otherwise indicated within thisdisclosure. For example, method 900 may be used in combination withmethod 500 and 600.

Method 900 may begin at 902 and may be initiated by an engine startingevent or a refueling event. A refueling event may comprise adding fuelto an externally filled fuel tank from an external source. A fuel systemequipped with a fuel separator may include a first outlet coupled to asecondary tank and a second outlet coupled to an externally filled fueltank. Fuel returned to the externally filled fuel tank may berecirculated back through the separator throughout operation,continuously removing low octane compounds from the fuel in theexternally filled fuel tank. Continued fuel separation may thus causethe fuel in the externally filled fuel tank to be depleted such that lowoctane fuel may not be available when desired. This may result inincreased emissions, decreased fuel efficiency, and may lessen theadvantages of the fuel separation system.

At 904 the level of fuel in the externally filled fuel tank may bedetermined and compared to a threshold. A threshold may be predeterminedor decided by a controller and may be equal to an amount of fuel withinthe low octane fuel tank. This may ensure low octane and high octaneavailability for optimal injection throughout the entirety of operationbefore a fuel refill. This may also help to combat fuel staleness.

At 908 the fuel may be delivered to a separator. At 910 the fuel withinthe separator may be separated into a high octane portion and a lowoctane portion. As described above, a separator may separate fuel basedon octane level. In other embodiments, fuel may be separated by otherfuel characteristics that result in one portion of the separated fuelhaving a higher octane level that the other portion of the separatedfuel. At 910 the high octane fuel and the low octane fuel may bephysically separated within the separator. In an embodiment, fuel may beseparated by a semi-permeable membrane, a physical barrier, a methodinvolving addition of water or other substance, or high octane fuel maybe in a more upper portion of the gasoline within the separator than lowoctane fuel or vice versa.

At 912, low octane fuel may be delivered to a low octane fuel tank. Insome embodiments, the high octane portion of the fuel separator may havea first outlet. High octane fuel may, in some embodiments, be releasedfrom the separator in a gaseous form. In such an embodiment, high octanefuel may be condensed into liquid form in a condenser separate from theseparator or within the separator.

In embodiments recirculating high octane fuel into an externally filledfuel tank, the high octane fuel tank may refer to the externally filledfuel tank.

At 912, low octane fuel may be delivered from a low octane outlet of afuel separator to a secondary low octane fuel tank. The low octane fueltank may be smaller than an externally filled fuel tank and may beindependently coupled to the engine. At 914 high octane fuel may bereturned to the externally filled fuel tank via a return line. In thisconfiguration a separator may produce high octane fuel at a higher ratethan low octane fuel. At 916, method 900 may repeat. After a number ofrepetitions of method 900, the octane level in the externally filledfuel tank may raise, effectively creating a high octane fuel tank. Theoctane level in an externally filled fuel tank may be proportional tothe duration of fuel separation.

In embodiments wherein an effective low octane fuel tank develops fromcontinued separation from the return of low octane fuel from anexternally filled fuel tank, the octane level of fuel in the externallyfilled fuel tank may be inversely proportional to the duration of fuelseparation. This may be true because the proportion of high octanecomponents to low octane components in the externally filled fuel tankmay shift with continued fuel separation.

FIG. 10 shows another example operating method in accordance with thepresent disclosure. Method 150 may be carried out by controller 12.Method 150 may be used in a configuration such as that depicted in FIGS.1-4. Method 150 may be used in combination or may be a subroutine ofmethods that may or may not be otherwise disclosed herein. For example,method 700 may be used in combination with method 500 and 600.

Method 150 may begin at 152 and may be initiated by an engine startingevent or a refueling event. A refueling event may comprise adding fuelto an externally filled fuel tank from an external source. In a fuelsystem equipped with a fuel separator with a first outlet coupled to asecondary tank and a second outlet coupled to an externally filled fueltank with a refuel port via a return line. Fuel returned to theexternally filled fuel tank may be recirculated back through theseparator throughout operation, continuously removing high octanecompounds from the fuel in the externally filled fuel tank. Continuedfuel separation may then cause the fuel in the externally filled fueltank to drop to a very low aggregate octane level. Fuel with extremelylow octane levels may not support even mid-range engine loads; resultingin degraded engine performance. Thus fuel in a high octane portion maybe used to support mid-load operation and the octane level within theexternally filled fuel tank may continue to fall with continuedseparation before triggering a re-fuel event which may result insignificant performance losses. Thus by monitoring the octane level inan externally filled fuel tank, separation may be terminated beforereaching an undesirably low octane level.

At 154 the octane level in the externally filled fuel tank may bedetermined and at 156 the octane level may be compared to a threshold. Athreshold may be predetermined or decided by a controller and may be anoctane level able to support mid-load operation. If the octane level offuel in the externally filled fuel tank is above a threshold the methodmay continue to 158. If the octane level of fuel in an externally filledfuel tank is below a threshold the method may end. The externally filledfuel tank may be fluidically coupled to a fuel separator and fuel may bedelivered to the separator at 158.

At 160 the fuel within the separator may be separated into a high octaneportion and a low octane portion. As described above, a separator mayseparate fuel based on octane level. In other embodiments fuel may beseparated by other fuel characteristics that result in one portion ofthe separated fuel having a high octane level that the other portion ofthe separated fuel. The high octane fuel and the low octane fuel may bephysically separated within the separator. In an embodiment fuel may beseparated by a semi-permeable membrane, a physical barrier, a methodinvolving addition of water or other substance, or high octane fuel maybe in a more upper portion of the gasoline within the separator than lowoctane fuel or vice versa.

At 162, high octane fuel may be delivered to a high octane fuel tank. Insome embodiments, the high octane portion of the fuel separator may havea first outlet. High octane fuel may, in some embodiments, be releasedfrom the separator in a gaseous form. In such an embodiment, high octanefuel may be condensed into liquid form in a condenser separate from thehigh octane fuel tank or within the high octane fuel tank.

In embodiments recirculating high octane fuel into an externally filledfuel tank, the high octane fuel tank may be the externally filled fueltank. Low octane fuel, as determined by the separator, may be returnedto an externally filled fuel tank via a return line. The cycle mayrepeat until the octane level in the externally filled fuel tank fallsbelow the aforementioned threshold. If the octane level in theexternally filled fuel tank falls below an octane threshold at 156, fuelseparation may end. Separation may be reinitiated in response to anengine refueling event. Engine separation may further be initiated by anengine starting event and may be terminated by an engine off event.

Presiding octane level in an externally filled fuel tank may bedetermined, in some embodiments, via a knock sensor system when fuelfrom the externally filled tank is being used. In other embodiments anoctane level may be inferred based on the amount of time separation hasoccurred, a volume of fuel through a separator or in a high octane fueltank. Other embodiments may determine a presiding octane level using asensor or method not otherwise disclosed herein.

At 164, low octane fuel may be returned to an externally filled fueltank via a return line. In some embodiments, the high octane portion ofthe fuel separator may have a second outlet. Low octane fuel may, insome embodiments, be released from the separator in a liquid form andreturned to the externally filled fuel tank. In such an embodiment, anexternally filled fuel tank may effectively become a low octane fueltank. The octane level of fuel within the externally filled fuel tankmay be inversely proportional to the duration of fuel separation. Thecontinued removal of high octane components from fuel of an externallyfilled fuel tank may cause the octane level of fuel to becomeincreasingly low.

At 166 a desired torque output may be determined. A desired torqueoutput may refer to an amount of torque desired from combustion withinthe engine as determined by a controller. An amount of torque desiredmay be a function of a number of operating conditions that may includeengine load, engine speed, or acceleration being requested by anoperator.

At 168 an octane level of fuel able to achieve the desired torque outputmay be determined. If a higher torque output is desired, a higher octanelevel of fuel injected into the engine may be desired.

In embodiments having an externally filled fuel tank receiving lowoctane fuel from a separator, the amount of high-octane-to-low-octanefuel ratio able to achieve a desired torque output may be dependent onthe presiding octane level of the fuel within an externally filled fueltank. At 170, an amount of high octane fuel used to dope fuel from anexternally filled fuel tank may be a function of the octane level in theexternally filled fuel tank and the octane level able to achieve thedesired torque output determined at 168.

At 172 it may be determined if high octane fuel is desired. This may bedetermined within a control system and may be responsive to an engineknock sensor, an engine load, or an engine temperature for example. Ifhigh octane doping of fuel delivered to the engine from the externallyfilled fuel tank is desired, the amount of high octane fuel determinedat 170 may be injected into a combustion chamber at 176. At 178 fuelfrom an externally filled fuel tank may be delivered to the combustionchamber. In other embodiments, high octane fuel may be injected into lowoctane fuel upstream of a combustion chamber, such as in a fuel rail ora fuel line. Other embodiments may inject fuel from an externally filledfuel tank using port injection and may inject fuel from a high octanefuel tank using direct injection. Method 150 may repeat throughoutengine operation.

FIG. 11 shows a flowchart depicting method 250 in accordance with thepresent disclosure. Method 250 may be carried out by controller 12.Method 250 may be used in a configuration such as that depicted in FIGS.1-4. Method 250 may be used in combination or may be a subroutine ofmethods that may or may not be otherwise indicated within thisdisclosure. For example, method 250 may be used in combination withmethod 500 and 600. Method 250 may be applied to an externally filledfuel tank, a low octane fuel tank, and/or a high octane fuel tank.Method 250 may be used to minimize fuel staleness by using fuel in afuel tank after a period of inactivity.

Method 250 may begin at 252. At 254 it may determined if the fuel tankis being used, in other words, if fuel from that tank is being injectedinto the engine. In this method a fuel tank may be any of the fuel tanksof the fuel system. For example, if the method is applied to a highoctane fuel tank then all references to the term fuel tank refer to thehigh octane fuel tank.

If fuel is being injected from the fuel tank a timer may be set to zeroat 256. A timer may be within a control system and may be a counter thatincreases at given time intervals and thus corresponds to an amount oftime elapsed since its most recent re-set or zero set.

At 258 it may be determined if the engine is on, engine on may refer tocombustion occurring within the engine. If combustion is not occurringthe engine may be considered off. If the engine is on at 258 the timermay be run with a weight. When the timer is run with a weight thecounter may be run at a faster pace. For example, for a given amount oftime, a counter being run with a weight may reach a higher value than atimer run without a weight. In other words, the time between counts maybe smaller when a counter is run with a weight. If the engine is not onthe method may continue to 260. At 260 the timer or counter may runwithout weight. In other words, for a given amount of time the counterwithout weight may reach a lower value than a counter with weight andthe amount of time between subsequent counts may be greater when thetimer is being run without weight. In some examples the weight may beone such that there is no difference in the frequency of counts when theweight is or is not applied. A weight greater than one may beadvantageous for measurements used to determine staleness. Fuel maybecome stale at an increased rate when the engine is running than whenthe engine is not running. For example, lighter components of gasolineevaporate at a higher rate at high temperatures which may be caused byengine operation, thus during engine operation fuel may become stalefrom evaporation more quickly. The weight given to a timer may beproportional to the increased rate at which fuel becomes stale duringengine operation than during engine off.

The value of the counter or timer may be compared to a threshold at 266.If the value is above a threshold method 250 may continue to 268. At 268fuel from the tank may be delivered to the engine for combustion. Insome embodiments fuel may be delivered to the engine continuously untilthe tank is empty. In other embodiments, an amount of fuel may beinjected into the engine or fuel from the tank may be delivered to theengine for a predetermined amount of time. The method may then return to256 where the timer may be set to zero. If the threshold is not met themethod may repeat indefinitely or until a refueling event.

FIG. 12 shows a flowchart depicting method 350 in accordance with thepresent disclosure. Method 350 may be carried out by controller 12.Method 350 may be used in a configuration such as that depicted in FIGS.1-4. Method 350 may be used in combination or may be a subroutine ofmethods that may or may not be otherwise indicated within thisdisclosure. For example, method 350 may be used in combination withmethod 500 and 600. Method 350 may refer to an externally filled fueltank, a low octane fuel tank, and/or a high octane fuel tank. Method 350may be used to minimize fuel staleness by monitoring the fuel stalenessin each tank independently and injecting fuel from that fuel tank intothe engine when fuel staleness is determined by a control system. Themethod may start at 352 and may be initiated by an engine refuelingevent or an engine starting event.

At 354, staleness from evaporation may be determined. In someembodiments, evaporation staleness may take a binary form (negative oraffirmative value), for example if evaporation is above a thresholdevaporation staleness is positive else it is negative. In otherembodiments evaporation staleness may have a numeric value, for examplefuel may be at 97% of accepted compound density.

Staleness from evaporation may refer to compounds within gasolineevaporating out of the fuel, particularly the lighter more volatilecomponents. This may cause engine performance losses, hard starting,increased emissions, and fuel efficiency losses. Further, this may lowerthe octane rating of the fuel. Staleness from evaporation may be afunction of temperature of the fuel throughout operation. For example,fuel may experience increased evaporation during higher temperatures. Inan embodiment, a weighted counter may run continuously after a refuelingevent. The weight of the counter may be proportional to temperature.Thus the temperature used in the determination of evaporation stalenessmay be representative of the temperatures experienced by the fuel forthe duration of its time in the fuel tank. Other embodiments maydetermine evaporation staleness based on the amount of time the fuel hasremained in the fuel tank, or the amount of time or flow through anevaporative emissions system, or the number of diurnal cycles. Stillfurther embodiments may directly determine evaporation staleness bymonitoring the density of components within the fuel or within the airin the fuel tank.

At 356, staleness from condensation may be determined. In someembodiments, condensation staleness may take a binary form (negative oraffirmative value), for example if water content is above a thresholdcondensation staleness may be positive, else it may be negative. Inother embodiments condensation staleness may have a numeric value, forexample fuel may be 12% water.

Staleness from condensation occurs when water contaminates fuel. Watercontamination may cause fuel line freezing or air-fuel ratio errors orpoor combustion stability or engine misfire. Water contamination occurswhen water in the air condenses into the fuel. This occurs mostfrequently when temperatures fluctuate. For example, if temperaturescool, humidity within the air may condense within a fuel tank and mixwith fuel. Water contamination may be determined in a controller and maybe responsive to an amount of time fuel has remained in a tank by amethod such as those mentioned above. Condensation staleness may furtherbe responsive to the number of diurnal cycles the fuel has been through,or the number of seasonal changes that have lapsed while the fuel was inthe fuel tank. The ambient humidity of air within the fuel tank, and thenumber of air changes due to diurnal cycles throughout the duration ofthe fuel being within the fuel tank may be monitored and may be used, inpart, to determine the condensation staleness of fuel.

Seasonal staleness or seasonal inappropriateness may be determined at358. In some embodiments, seasonal staleness may take a binary form(negative or affirmative value), for example if more than six monthshave elapsed since a refueling event, seasonal staleness may be positiveelse it may be negative. Gasoline distributed for consumers may have asummer grade chemical composition or a winter grade chemicalcomposition. Appropriate grade fuel may help to improve engine startingduring cold winter months and decrease emissions or avoid vapor lockduring warm summer months. Seasonal staleness may be determined orinferred based on the time elapsed since a last refueling event, achange in ambient temperature, and/or the chemical composition of fuelsuch as an amount of butane per unit volume. Note seasonal staleness maynot imply fuel degradation.

Oxidation staleness may be determined at 360. Oxidation staleness mayrefer to oxygen reacting with the hydrocarbons within the fuel to formother compounds. These compounds may dramatically change the chemicalcomposition of the fuel, lowering the fuel volatility or energy density.Severe oxidation may cause the fuel to coagulate or form deposits.Coagulated fuel or deposits may clog fuel lines, fuel filter, fuelinjectors, or other components in the fuel system. Oxidation stalenessmay be determined in response to fuel volatility or the number of airchanges due to diurnal cycles or an amount of time fuel has been in thefuel tank.

Drain down may be determined at 362. When fuel sits for an amount oftime, fuel may drain from the lines back into the tank or other fuelsystem components, and air bubbles may form in the fuel lines due toimperfect sealing at injectors or fuel system connections, or due topermeation through fuel system components. Air bubbles in fuel lines mayresult in injection of less fuel than desired, causing degradedemissions or engine misfire. Drain down may be determined as a functionof an amount of vibration the fuel has experienced since the fuel lineshave been purged via injection of fuel in the relevant fuel tank. Thisvibration may itself be inferred within a control system from an amountof time or miles driven since a fuel line purge, or it may be sensed byaccelerometers. In one embodiment, accelerometer signals normally usedfor vehicle stability control or other purposes may be used in the draindown calculation. In another embodiment, vehicle location informationmay be used in conjunction with data about road roughness for the draindown calculation.

At 364 it may be determined if fuel staleness is above a threshold. Fuelstaleness may be a function of evaporation staleness, condensationstaleness, seasonal staleness, oxidation staleness, or some combinationthereof. In some embodiments, each staleness may be compared to athreshold or binary comparator, if one or more of the stalenessindicators are above the threshold or have an affirmative binary value,the threshold may be met at 364. Staleness may refer to evaporationstaleness, condensation staleness, oxidation staleness, seasonalappropriateness, or fuel drain down.

If the threshold is met at 364, fuel from the stale fuel tank may bedelivered to the engine. Here delivery from the stale fuel tank mayrefer to increasing a rate at which the fuel from the stale tank is usedor injecting fuel from the fuel stale tank until the tank is empty. Insome embodiments, fuel may be purged or an indicator set. In stillfurther examples, a rate at which fuel is injected from a stale tank mayincrease gradually with fuel staleness. In some examples fuel separationmay be suspended until the stale fuel has been purged from the tank.

If the fuel is not stale at 364, the method may go to 368. At 368 it maybe determined if drain down is above a numeric threshold or indicated.If drain down is found to be above a threshold, an amount of fuel fromthe drain down tank may be delivered to the engine. Drain down may berectified by purging the line of air bubbles by injecting enough fuelinto the engine so that air bubbles or purged, or until all fuel withinthe fuel line or fuel rail is replaced by fuel within the tank. Thus, at370 a sufficient amount of fuel from the drain down tank may bedelivered to the engine. The method may repeat at given intervals oftime or distance traveled. In some embodiments, method 350 may be asubroutine of method 250. For example, if the timer is above a thresholdat 266, method 350 may be initiated.

In still further embodiments, fuel from each fuel tank may be injectedintermittently into the engine. For example, fuel from each fuel tankmay be injected after an engine starting event or at predeterminedintervals. Thus fuel in an underused tank is regularly injected so thatfuel in an underused tank does not sit indefinitely.

In other embodiments an engine may have a staleness prevention mode thatmay be initiated periodically, in response to an engine starting event,or in response to a refueling event. In a staleness prevention mode,equal amounts of fuel from each of the tanks coupled to the engine, oramounts proportional to the tank sizes, may be injected into the enginefor combustion. In some embodiments this may occur over a predeterminedamount of time or until a predetermined amount of fuel is injected intothe engine. In other embodiments staleness prevention mode may beinitiated immediately or soon following an engine starting event.

For example, if a system having a high octane and low octane fuel tankenters a staleness prevention mode, equal amounts of high octane fueland low octane fuel may be delivered to the engine for combustion. Orthe amounts of high octane fuel and low octane fuel may be proportionalto the size of the high and low octane fuel tanks respectively. This maycontinue for a predetermined amount of time or until a predeterminedamount of fuel is injected, staleness prevention mode may then end andnormal operation and fuel injection ensue. In still further embodimentsof a staleness prevention mode, an amount of fuel in a high octane fueltank may be compared to a level of fuel in a low octane fuel tank, ifthe high-octane-to-low-octane fuel level ratio is above a firstthreshold, high octane fuel may be injected at a high rate until thefuel level falls below a second threshold. Similarly, if the high octaneto low octane fuel level is below a third threshold, low octane fuel maybe injected at a high rate until the fuel level reaches a fourththreshold.

FIG. 13 shows a flowchart depicting method 450 in accordance with thepresent disclosure. Method 450 may be carried out by controller 12.Method 450 may be used in a configuration such as that depicted in FIGS.1 and 4. Method 450 may be used in combination or may be a subroutine ofmethods that may or may not be otherwise indicated within thisdisclosure. For example, method 450 may be used in combination withmethod 500 and 600.

Method 450 may be used in a system equipped with secondary air injectionand fuel separation. Secondary air injection may deliver atmospheric airto an exhaust manifold. This may allow faster catalyst light-off and maylower emissions. A fuel system may split fuel into a low octane portionand a high octane portion. In some embodiments, low octane fuel may berecirculated back into an externally filled fuel tank and high octanefuel may be stored in a secondary tank or vice versa. In theseembodiments, both an externally filled fuel tank and a secondary fueltank may be individually coupled to the engine. In other embodiments,both the high octane fuel and the low octane fuel may be storedseparately in two secondary fuel tanks. In some embodiments the two fuellines may merge upstream of direct injectors or port injectors so thatlow octane fuel and high octane fuel are combined upstream of theinjector. In other embodiments, the low octane fuel tank and high octanefuel tank may be fluidically coupled to independent direct and/or portinjectors such that high octane fuel and low octane fuel are combinedafter injection. In embodiments having two secondary (high and lowoctane) fuel tanks and an externally filled fuel tank, each of the threefuel tanks may be independently coupled to direct injectors and/or portinjectors. One or more of the fuels may merge in a fuel line upstream ofan injector.

Method 450 may begin at 452 and may be initiated by an engine startingevent. At 454 it may be determined which of the fuels is most desirablefor secondary air injection. In other words, it may be determined whichof the fuels contains hydrocarbons most likely to oxidize duringsecondary air injection. This may be inferred based on an octane levelof the fuels, for example, low octane fuel may be assumed more desirablefor secondary air injection. Other embodiments may determine which fuelis desirable in response to an amount of time separation has occurredand may further infer the octane level of fuel based on the duration ofseparation. Further embodiments may measure octane level directly or viaa knock feedback sensor. Other embodiments may directly measure therelevant properties of a fuel which may be correlated with the fuelsoxidation properties; this may include vapor pressure, density,capacitance, molecular weight, and refractance. It some embodiments itmay be determined that no fuel is desirable for oxidation. This mayresult after a fuel refill event before fuel is adequately separated. Insome embodiments, the desirable fuel for secondary air injection asdetermined above may define an engine condition. For example, in a firstcondition, the fuel determined to be desirable for combustion duringsecondary air injection may be the high octane fuel. In a secondcondition, the fuel determined to be desirable for combustion duringsecondary air injection may be the low octane fuel.

At 456 it may be determined if the desirable fuel is currently beinginjected into engine for combustion. In other words, if the engine is ina first condition it may be determined if high octane fuel is currentlybeing injected for combustion. In a second condition it may bedetermined if low octane fuel is being injected for combustion.

If the desirable fuel is being used, it may be determined if secondaryair injection is desired at 458. This may be in response to a cold startcondition when catalyst warm-up is desired, and other conditions arefavorable for use of secondary air.

If secondary air injection is desired at 458, secondary air injectionmay be initiated at 460 by injecting air into the exhaust system orexhaust manifold. Within the exhaust system or manifold hydrocarbons mayinteract with injected oxygen for continued combustion and reducedemissions. In some embodiments additional heat may be delivered to theexhaust system for increased secondary combustion. At 462 the method mayrepeat. The method may repeat in rapid succession or at predeterminedintervals.

FIG. 14 shows a flowchart depicting method 550 in accordance with thepresent disclosure. Method 550 may be carried out by controller 12.Method 550 may be used in a configuration such as that depicted in FIGS.1 and 4. Method 550 may be used in combination or may be a subroutine ofmethods that may or may not be otherwise indicated within thisdisclosure. For example, method 550 may be used in combination withmethod 500 and 600.

Method 550 may be used in a system equipped with secondary air injectionand fuel separation. Secondary air injection may deliver atmospheric airto an exhaust manifold. This may allow faster catalyst lightoff and maylower emissions. A fuel system may split fuel into a low octane portionand a high octane portion. In some embodiments, low octane fuel may berecirculated back into an externally filled fuel tank and high octanefuel may be stored in a secondary tank or vice versa. In theseembodiments, both an externally filled fuel tank and a secondary fueltank may be individually coupled to the engine. In other embodiments,both the high octane fuel and the low octane fuel are stored separatelyin two secondary fuel tanks. In some embodiments the two fuel lines maymerge upstream of direct injectors or port injectors so that low octanefuel and high octane fuel are combined upstream of the injector(s). Inother embodiments, the low octane fuel tank and high octane fuel tankmay be fluidically coupled to independent direct and/or port injectorssuch that high octane fuel and low octane fuel are combined afterinjection. In embodiments having two secondary (high and low octane)fuel tanks and an externally filled fuel tank, each of the three fueltanks may be independently fluidically coupled to direct injectorsand/or port injectors. One or more of the fuels may merge in a fuel lineupstream of an injector.

The method may begin at 552 and may be initiated by the initiation ofsecondary air injection. At 554 it may be determined which of the fuelsis most desirable for combustion during secondary air injection. Inother words, it may be determined which of the fuels containshydrocarbons most likely to oxidize during secondary air injection. Thismay be inferred based on an octane level of the fuels, for example, lowoctane fuel may be assumed more desirable for secondary air injection.Other embodiments may determine which fuel is desirable in response toan amount of time separation has occurred and may further infer theoctane level of fuel based on the duration of separation. Furtherembodiments may measure octane level directly or using a knock feedbacksensor. Other embodiments may directly measure the relevant propertiesof a fuel which may be correlated with the fuels oxidation properties;this may include vapor pressure, density, capacitance, and refractance.It some embodiments it may be determined that no fuel is desirable foroxidation. This may result after a fuel refill event before fuel isadequately separated.

In some embodiments, the type of fuel found to be most desirable maydefine an engine condition. In a first condition, high octane fuel maybe determined more desirable for combustion during secondary airinjection. In a second condition low octane fuel may be found to be moredesirable for combustion during secondary air injection.

At 556 it may be determined if the desirable fuel is currently beinginjected into the engine for combustion. For example, it may bedetermined if, in a first condition, high octane fuel is being injectedinto the engine or, in a second condition, low octane fuel is beinginjected into the engine. It may be determined if the presidingoperating conditions are sustainable with the desired fuel at 558. Thismay include the amount of desirable fuel available, presiding engineload, speed, temperature, knock suppression, or emission production.

If the desirable fuel is not being injected but the current operatingconditions may be sustained using the desirable fuel, the desirable fuelmay be injected into the engine for combustion at 560. In alternateembodiments, the percentage of desirable fuel to undesirable fuelinjected may increase. The desirable fuel may be more readily oxidizedthan the currently injected fuel. The desirable fuel may thus demandless spark retard for acceptable oxidation and increased exhaust heat.

In a conditional example, if the engine is found to be in a firstcondition and high octane fuel is not being injected into the engine, itmay be determined at 558 if operating conditions are sustainable withthe injection of high octane fuel. If sustainability with high octanefuel is determined, high octane fuel may be delivered to the engine andused for combustion and a first operating routine may be initiated. Ifit is determined that operating conditions cannot be sustained with thehigh octane fuel, low octane fuel may continue to be injected into theengine and a second routine may be initiated.

Further, if the engine is found to be in a second condition and lowoctane fuel is not being injected into the engine, it may be determinedat 558 if operating conditions are sustainable with the injection of lowoctane fuel. If sustainability with low octane fuel is determined, lowoctane fuel may be delivered to the engine and used for combustion and afirst operating routine may be initiated. If it is determined thatoperating conditions cannot be sustained with the low octane fuel, highoctane fuel may continue to be injected into the engine and a secondroutine may be initiated.

Thus, the step 562 may be referred to as a first routine. In a firstroutine, the amount of spark retard may be decreased. In someembodiments fuel enrichment, that may have been increased to achieveefficient secondary combustion, may be decreased at 562 or in a firstroutine. An amount of air delivered to the exhaust system for secondaryair injection may also be decreased. In embodiments having additionalheat source applied to the exhaust system, additional heat delivered tothe exhaust system may be decreased or suspended at 562 or in a firstroutine. Further, if a presiding AFR has been decreased to promotesecondary combustion, it may be increased to a level determined by theoperating conditions. Returning to 558, if the operating conditions arenot sustainable with the desirable fuel the method may end at 570.

If it is determined at 556 that the desirable fuel is being injected themethod may continue to 564. At 564 it may be determined if the presidingoperating conditions are sustainable with continued use of the desirablefuel. This may include the amount of desirable fuel available, presidingengine load, speed, temperature, knock suppression, or emissionproduction. If operation may be sustained with the desirable fuel, themethod may proceed to 560 as previously described. If the operatingconditions cannot be maintained with the desirable fuel, the undesirablefuel may be injected into the engine for combustion at 566 and a secondroutine may be initiated. In alternate embodiments, the percentage ofundesirable fuel to desirable fuel injected may increase. If undesirablefuel is injected at 566, in a second routine, spark retard may beinitiated or increased. Increased spark retard may increase thetemperature of exhaust gas to allow for secondary air injection of theless readily oxidized fuel. An amount of enrichment and/or an amount ofair delivered to the exhaust system for secondary air injection may alsobe increased in a second routine. In embodiments having additional heatsource applied to the exhaust system, additional heat delivered to theexhaust system may be increased or initiated at 568.

Method 550 may be initiated in response to initiation of secondary airinjection. Secondary air injection may be initiated in response tomethods that may or may not be otherwise disclosed herein. Method 550may continue while secondary air injection continues and may besuspended when secondary air injection stops.

FIG. 15 shows a flowchart depicting method 650 in accordance with thepresent disclosure. Method 650 may be carried out by controller 12.Method 650 may be used in a configuration such as that depicted in FIGS.1 and 4. Method 650 may be used in combination or may be a subroutine ofmethods that may or may not be otherwise indicated within thisdisclosure. For example, method 650 may be used in combination withmethod 500 and 600.

Method 650 may be used in a system equipped with secondary air injectionand fuel separation. Secondary air injection may deliver atmospheric airto an exhaust manifold. This may allow faster catalyst lightoff and maylower emissions. A fuel system may split fuel into a low octane portionand a high octane portion. In some embodiments, low octane fuel may berecirculated back into an externally filled fuel tank and high octanefuel may be stored in a secondary tank or vice versa. In theseembodiments, both an externally filled fuel tank and a secondary fueltank may be individually coupled to the engine. In other embodiments,both the high octane fuel and the low octane fuel are stored separatelyin two secondary fuel tanks. In some embodiments the two fuel lines maymerge upstream of direct injectors or port injectors so that low octanefuel and high octane fuel are combined upstream of the injector. Inother embodiments, the low octane fuel tank and high octane fuel tankmay be fluidically coupled to independent direct and/or port injectorssuch that high octane fuel and low octane fuel are combined afterinjection. In embodiments having two secondary (high and low octane)fuel tanks and an externally filled fuel tank, each of the three fueltanks may be independently fluidically coupled to direct injectorsand/or port injectors. One or more of the fuels may merge in a fuel lineupstream of an injector.

The method may begin at 652 and may be initiated by an engine startingevent. At 654 it may be determined which of the fuels is most desirablefor combustion during secondary air injection. In other words, it may bedetermined which of the fuels contains hydrocarbons most likely tooxidize during secondary air injection. In a first condition, the highoctane fuel may be the desirable fuel. In a second condition, the lowoctane fuel may be the desirable fuel. A desirable fuel may be inferredbased on an octane level of the fuels, for example, low octane fuel maybe assumed more desirable for secondary air injection. Other embodimentsmay determine which fuel is desirable in response to an amount of timeseparation has occurred and may further infer the octane level of fuelbased on the duration of separation. Further embodiments may measureoctane level directly or using a knock feedback sensor. Otherembodiments may directly measure the relevant properties of a fuel whichmay be correlated with the fuels oxidation properties; this may includevapor pressure, density, capacitance, and refractance. In someembodiments it may be determined that no fuel is desirable foroxidation. This may occur after a fuel refill event when fuel is notadequately separated.

At 656 it may be determined if the engine is operating in a cold startcondition. In other embodiments this may be responsive to thetemperature of the engine or catalyst, or the atmospheric temperature,it may be further responsive to the amount of time the engine isoperating. If a cold start is determined at 656, it may be determined at658 if the desirable fuel, as determined at 654, is available forinjection. This may be determined by a sensor within a fuel tank thatmay measure the fuel level and fuel properties. If the desirable fuel isavailable the desirable fuel may be injected into the engine forcombustion at 662. Injection of the desirable fuel may continue for apredetermined amount of time, for the duration of secondary airinjection, or it may continue while an engine or catalyst temperature ismeasured or inferred to be under a threshold. At 664 a first cold startroutine may be initiated. The first routine may include a first degreeof spark retard, a first AFR, and/or a first amount of secondary airinjection.

For example, in a first condition, if high octane fuel is injected intothe engine at 662 the first routine may be initiated at 664. In a secondcondition, if low octane fuel is injected into the engine at 662, thefirst routine may also be initiated at 664.

If at 658 it is determined that the desirable fuel is not available, adifferent fuel may be injected into the engine and a second cold startroutine initiated at 660. The second routine at 660 may include a seconddegree of spark retard, a second AFR, and/or a second amount ofsecondary air injection. The second degree of spark retard may begreater than the first degree of spark retard and the second AFR may belower than the first AFR. The method may end at 666. In otherembodiments the method may repeat at given intervals or in rapidsuccession.

In other words, in a first condition, if low octane fuel is injectedinto the engine, a second routine may be initiated. In a secondcondition, if high octane fuel is being injected into an engine, asecond routine may also be initiated.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The specific routines described herein may represent one or more of anynumber of processing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various actions,operations, and/or functions illustrated may be performed in thesequence illustrated, in parallel, or in some cases omitted. Likewise,the order of processing is not necessarily required to achieve thefeatures and advantages of the example embodiments described herein, butis provided for ease of illustration and description. One or more of theillustrated actions, operations and/or functions may be repeatedlyperformed depending on the particular strategy being used. Further, thedescribed actions, operations and/or functions may graphically representcode to be programmed into non-transitory memory of the computerreadable storage medium in the engine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

The invention claimed is:
 1. An engine method, comprising: deliveringhigh octane fuel to a high octane fuel tank and delivering low octanefuel to a low octane fuel tank, wherein the high octane fuel has ahigher octane rating than the low octane fuel; injecting high octanefuel into an engine using a first routine or low octane fuel using asecond routine in response to a first condition and secondary airinjection; and injecting low octane fuel into the engine using the firstroutine or high octane fuel using the second routine in response to asecond condition and secondary air injection.
 2. The engine method ofclaim 1, further comprising, during secondary air injection, pumpingatmospheric air from an air intake into an exhaust system.
 3. The enginemethod of claim 1, further comprising combusting an amount of unburnthydrocarbons within exhaust gas following secondary air injection. 4.The engine method of claim 1, further comprising determining if highoctane fuel is desirable or if low octane fuel is desirable in responseto a molecular weight, volatility, vapor pressure, refractance,capacitance, density, octane level, or some combination thereof, of thehigh octane fuel and the low octane fuel.
 5. The engine method of claim1, wherein the first routine is implemented under the second conditionin response to operating conditions being unsustainable with high octanefuel or an unavailability of high octane fuel; and the second routine isimplemented under the second condition in response to operatingconditions being unsustainable with low octane fuel or an unavailabilityof low octane fuel.
 6. The engine method of claim 1, wherein the secondroutine includes increasing an amount of spark retard or decreasing anAFR in response to the second routine being implemented.
 7. The enginemethod of claim 1, wherein in the first condition, using the firstroutine comprises injecting the high octane fuel to the engine if highoctane fuel is not being injected into the engine, and using the secondroutine comprises continuing to inject low octane fuel into the engine;and wherein in the second condition, using the first routine comprisesinjecting the low octane fuel to the engine if low octane fuel is notbeing injected into the engine, and using the second routine comprisescontinuing to inject high octane fuel into the engine.